If you teach a class on treating hypothermia in the wilderness you are bound to be asked about the value of a warm person snuggling with a cold person in a sleeping bag. Actually, snuggling may not be the best word, because putting aside the giggles this conversation elicits in some audiences it’s not easy to hug a physically cold person and the snuggling is a necessary task, not a recreational experience. But, that’s not what I want to write about. I want to discuss whether it’s helpful to put a warm person into a sleeping bag with a cold person.

Body-to-body warming hasn’t seen much research. It seems the technology of heaters and forced air warming is more attractive. The research we found says it doesn’t help much, and it probably doesn’t harm. 1,2

According to Gordon Giesbrecht an adult cooled to 95∞F (34.7∞C), the common threshold for hypothermia definitions, can have a profound caloric deficit. 2 A healthy adult at rest will make about 1kcal of heat per kg of body weight per hour. This won’t be enough to quickly reverse significant hypothermia. In those tales where we got in a sleeping bag and heroically warmed the severely cold person – well - we may have done the patient a favor, but they probably were not very cold in the first place.

Ideally the people should be nude. The more skin to skin contact the better, but realistically, even nude, the direct skin contact between the heat donor and the patient is small.

According to Dr Giesbrecht3 the transfer of the energy to the core will be blunted by vasoconstriction. Since most of our mildly hypothermic patients are not dramatically vasoconstricted, this will be only a small hindrance. In severely hypothermic patients it may be a significant limitation to the heat transfer from donor to recipient.

We know that shivering is a powerful means, indeed our best wilderness tool to produce heat in a person with the energy reserves to shiver. We also know that warming the skin blunts the shivering response. We don’t know the significance of the shivering inhibition from warming skin because, even if the patient shivers less, they feel more comfortable and preserve their energy reserves (e.g. they burn fewer calories shivering).

There is concern the donor may become hypothermic. I’ve seen heat donors realize this isn’t a lot of fun, but in the real world, and in the research, the donors don’t become hypothermic.

What are the positives of putting another person in the bag?

It may provide comfort for the patient to snuggle with another person.

You can monitor the patient closely.

You may help the patient warm while they expend fewer calories shivering.

If the patient is unable to shiver, perhaps they are severely cold, metabolically exhausted, or unable to shiver, the second person in the bag may at least warm the insulation, the thermos bottle of the hypo wrap, and help keep the patient from cooling further, a very important goal.

What are the negatives?

You may not be able to fit the heat donor in the bag and still close the opening tightly. This may reduce the effectiveness of the hypo wrap.

If you plan on carrying the patient with the heat donor inside you’ll have the weight of two to manage.

The donor may jostle the severely cold patient, who we want to treat as gently as possible.

The heat donor is not on the surface doing important tasks such as building a fire, making sure your companions are also not hypothermic. Preparing shelter, hot drinks and food.

When the heat donor has tired of being in the wrap and wants out the nice cocoon has to be opened.

We’re often asked about the donor sweating and wetting the insulation. Yes, it can become steamy in there, but wet insulation has not been a problem in our experience.

What should we do?

Most of our “hypothermic” patients in the wilderness are not hypothermic in a medical sense, that is, they are warmer than 95F (34.7C). The people we think of as hypothermic are cold challenged, cold stressed, cold and unhappy. However, our world is not the controlled hospital environment. This situation gets our immediate attention. We’ll attend to the cold person promptly, and if they are healthy, we’ll warm them by removing them from the cold stress, placing them in dry clothing and dry insulation, such as a sleeping bag, and feeding and hydrating them. Their internal metabolic fires, shivering, and our tender loving care will warm their heart, and their body.

People who are truly hypothermic are dangerously ill. They may be wasted (a non medical term that says they are fatigued, dehydrated and low on food reserves), or have a serious simultaneous medical condition. We may not be able to warm these people in the backcountry. Our efforts are focused on stabilizing the patient; we don’t want to jostle them or allow them to cool further. They likely will only warm in the hospital, so we transport them gently

I’ve been told two people in a sleeping bag to treat hypothermia is the “standard of care” in the wilderness. Actually, it’s not. The science isn’t strongly in it’s favor and in the wilderness, scenarios are often unique, our equipment less than ideal and our need to improvise real. As always, we’ll use our judgment, understand the principles of treatment and weight the factors in our specific scenario. The heat sources you have available on your wilderness trip may only be insulated hot water bottles, or the patient’s metabolism and shivering. If you have a good camp and plenty of people you may be able to spare a person to be in the sleeping bag. If you’re a small group, and knowing heat transfer between bodies is not very efficient, you may decide your assistant is best used staring a fire, making a warm meal and drink on the stove, setting up the camp or attending to the other people on your trip.